Top journal touts 'gecko' technology

10/10/2008

The University of Akron continues to build on its reputation for cutting-edge research based on geckos.

Science - the world's leading journal of original scientific research, global news and commentary - has published the findings of groundbreaking, dry-adhesive nanotechnology research conducted by a four-member scientific team that includes The University of Akron's Dr. Zhenhai Xia, assistant professor of mechanical engineering. This new technology is three times more powerful than any previously developed adhesive technology.

Based on its studies of the fine hairs that grow on the soles of gecko feet, the team reported that carbon nanotube arrays create an adhesive nearly 10 times stronger than the microscopic hairs that grow at the base of a gecko's feet and toes.

Strong bond, yet simple removal

In collaboration with researchers from the University of Dayton, the Air Force Research Laboratory at Wright-Patterson Air Force Base and Georgia Institute of Technology, Xia developed both the theoretical analysis and the computer simulation to explain the team's experimental results and to discover the new mechanism. Their discovery, an array of minuscule fibers each about 1/50,000th the width of human hair strands, create a nonliquid adhesive with magnetic force, yet simple removal.

"Geckos have fascinated generations of researchers with their extraordinary ability to move on vertical surfaces and ceilings. They climb on wet or dry, smooth or rough, vertical and even inverted surfaces with ease, rapidly switching between attachments and detachments," Xia says. "After many endeavors, we have obtained experimental evidence to conclude that short-range, weak-to-strong forces are the dominating mechanisms behind this adhesion."

Xia explains that the primarily straight nanotubes have curly, entangled tops, similar to the lizard-foot hairs, but better. Set in arrays, the nanotubes create a shear adhesion force much stronger than normal adhesion force, which ensures strong binding (along the shear direction) and easy lifting in the normal direction, making it possible to simulate the walking of a living gecko.

Practical applications

"The new gecko-mimetic adhesives are promising in various applications, such as climbing robots, reusable tapes, super-grip tires and rapid patch repairs on military vehicles," Xia says. "Because carbon nanotubes conduct heat and electrical current, the dry adhesive arrays could be used to connect electronic devices. They could also be used in space. With the gecko-foot mimetic dry adhesives, the dream of Spider-Man could become truth, but we have a long way to go."

"This is significant research with real-world applications that will affect consumers worldwide," says Dr. George Haritos, dean of the UA College of Engineering. "Moreover, because this new adhesive would not be compromised by drying out in a vacuum environment, it certainly appears promising for use in space exploration."

University of Akron scientists have long been involved in gecko research and have contributed greatly to advancements in nanotechnology that mimics the binding qualities of the microscopic hairs on these lizards' feet and toes.

This current study, "Carbon Nanotube Arrays with Strong Shear Binding-On and Easy Normal Lifting-Off," is available at www.sciencemag.org.

The journal Science is published by the American Association for the Advancement of Science, an international nonprofit organization dedicated to advancing science around the world by serving as an educator, leader, spokesperson and professional association.